1. Field of the Invention
The present invention relates to a starter for starting an engine.
2. Description of the Prior Art
FIG. 11 is a cross-sectional view showing one example of a conventional starter disclosed in Japanese laid-Open Patent Application (Kokai) No. Hei 10-159692.
In FIG. 11, reference numeral 1A is an output shaft. Coaxially arranged on this output shaft 1A are an electromagnetic switch 2A, an overrunning clutch 30A provided with a pinion 30P for engaging with a ring gear 50A, a plunger 40A consisting of an inner plunger 4A and an outer plunger 4B, etc. A starter with this structure is generally called a coaxial type starter.
Reference numeral 12A is an armature of a DC motor and 16A is a shaft (a motor shaft). 18A is a deceleration mechanism for decelerating the turning force of the shaft 16A and transmitting the decelerated force to the output shaft 1A. 8A is a contact shaft which is supported substantially parallel with the plunger 40A by an internal gear member 17A of the deceleration mechanism 18A through a supporting hole 17m.
100 is a bracket, and 800 is a shift plate for connecting the outer plunger 4B to the contact shaft 8A.
Further, the upper side of the central axis in FIG. 11 shows the state where the starter is not put in operation, and the lower side of the central axis in FIG. 11 shows the state where the starter is in operation with an electromagnetic switch turned ON and the pinion is caused to engage with the ring gear.
Operation will now be explained hereunder. Operation is explained with reference to FIG. 12 which is a partially enlarged view of FIG. 11.
When an ignition switch is turned ON and an electric current flows to an exciting coil 2B of the electromagnetic switch 2A, the outer plunger 4B is attracted by an exciting core 2C of the electromagnetic switch 2A. This conventional starter has such a structure that the outer plunger 4B is directly connected to the contact shaft 8A through the shift plate 800, and the contact shaft 8A also moves at the same time when the outer plunger 4B is attracted and moved by the exciting coil 2B. A coil spring 401 is disposed between the outer plunger 4B and the inner plunger 4A through a spring bearing member 400. The inner plunger 4A is kept in the resting state because the coil spring 401 compresses at the initial stage even if the outer plunger 4B starts the attraction movement. Disposed in front of the inner plunger 4A through a shifter member 402 is an inner clutch 30B, which is also kept in the resting state while the inner plunger 4A is kept in the resting state. After a short interval when the outer plunger 4B starts the attraction movement, a moving contact 80A mounted on the contact shaft 8A comes into contact with a stationary contact 80B disposed in a contact chamber ZA. When the moving contact 80A contacts with the stationary contact 80B, electric power is supplied from an external power source through a contact bolt 11A to start rotation of the armature 12A. When the output shaft 1A starts to turn through the deceleration mechanism 18A, the pinion 30P starts to move toward the ring gear 50A by the thrust generated in a helical spline portion 1B. Then, the crests and roots of the pinion 30P agree and engage with those of the ring gear 50A. Thereafter, when the engine starts, the output shaft 1A is disengaged from the pinion 30P by the action of the overrunning clutch 30A and the pinion 30p runs idle. When the power supply to the exciting coil 2B is stopped, the pinion 30P is disengaged from the ring gear 50A by return springs 403 and 404.
In the conventional starter disclosed in Japanese Laid-Open patent Application (Kokai) No. Hei 10-159692, the outer plunger 4B is directly connected to the contact shaft 8A through the shift plate 800. Since the contact shaft 8A also moves simultaneously as the outer plunger 4B is attracted and moved, the moving contact 80A immediately comes into contact with the stationary contact 80B. The armature 12A begins to rotate before the end surface 30Pe of the pinion 30P comes into contact with the end surface 50Ae of the ring gear 50A.
In other words, according to the above-mentioned starter, the pinion 30P is caused to rotate by driving the armature 12A before the pinion 30P engages with the ring gear 50A. However, in the above starter, the driving force by the thrust generated in the helical spline portion 1B is insufficient to press the pinion 30P toward the ring gear 50A and the coil spring 401 is also incapable of pressing the pinion 30P toward the ring gear 50A. Therefore, when engaging with the ring gear 50A, the pinion 30P is often repelled by the ring gear 50A and tries to engage with it.
Accordingly, the pinion 30P does not engage with the ring gear 50A smoothly and the reliability when the pinion 30P engages with the ring gear 50A is low. In addition, the gears are worn away and the life span of the gears is shortened.
As described above, the conventional starter has such a structure that the contact shaft moves by the same amount as the (outer) plunger does. In this case, it is necessary to secure a moving space of a plate (retaining ring etc) 9A for holding the coil spring 9S adapted to press both the contact shaft and the moving contact inside the contact chamber. As a result, the contact chamber inevitably becomes large.
Also, when the clearance between the contact shaft and the supporting portion therefor is large, the backlash is caused therebetween and affects the sliding of the contact shaft to make the contact of the moving contact with the stationary contact imperfect. It may cause contact failure. On the contrary, when the clearance is small, it may cause wearing.